Laser Diode Assemblies

ABSTRACT

Laser diodes ( 120 ) emit laser beams along a vertical YZ plane at different distances from the YZ plane. The beams are collimated in their fast and slow axes, and are redirected by turning mirrors ( 162 ) to form a beam stack ( 130 C) traveling along the XZ plane. The beam stack is turned by about 90°, then converged by a focusing lens ( 174 ) into an optical fiber ( 180 ). A compact assembly is thus provided. Each laser diode ( 120. i), its collimating optics ( 154. i,  158. i, i= 1,2, . . .  ) and its turning mirror ( 162. i) are rigidly attached to a flat, heat-spreading surface ( 144. i) and thus remain aligned with each other in thermal cycling.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 12/058,459, filed 28 Mar. 2008, incorporated herein byreference.

BACKGROUND OF THE INVENTION

The present application is a continuation of U.S. patent applicationSer. No. 12/058,459, filed 28 Mar. 2008, incorporated herein byreference.

The present invention relates to laser diode assemblies.

Laser diodes offer both high output power and a small footprint, makingthem good candidates for many applications including materialsprocessing, medical devices, telecommunications, printing, and otheruses. The output of the laser diode can be coupled to an optical fiberserving as a waveguide or providing a laser cavity for a fiber laser.The optical fiber's input surface is typically circular, while the laserdiode's output beam is roughly an elongated rectangle. Therefore, directcoupling of the output beam into the fiber is inefficient,underutilizing the fiber's input area and hence the fiber's capacity forinput brightness and power.

To increase the brightness and power coupled into the fiber, outputbeams of multiple laser diodes can be stacked above each other (i.e.with the long axes stacked above each other) to more closely approximatea circle. The long axis of a laser diode's emitter is called a “slowaxis” due to low divergence of the beam along this axis. This axis isparallel to the diode's pn junction. The emitter' short axis, which iscalled a “fast axis” due to higher divergence of the beam along thisaxis, is perpendicular to the pn junction. For manufacturingconvenience, the laser diodes can be manufactured in a singlesemiconductor structure in a laser diode bar configuration, with theirslow axes positioned on a single line, and the beams can be placed intoa stack using turning mirrors. See e.g. U.S. Pat. No. 6,044,096 issuedMar. 28, 2000 to Wolak et al. See also U.S. Pat. No. 6,898,222 issuedMay 24, 2005 to Hennig et al., describing another configuration in whichthe laser diodes' slow axes are not on a single line to form a steppedconfiguration.

Even minute misalignments between the laser diodes and the opticalcomponents (such as turning mirrors and the collimating and focusingoptics) may reduce the coupling efficiency between the laser diodes andthe optical fiber.

SUMMARY

This section summarizes some features of the invention. Other featuresare described in the subsequent sections. The invention is defined bythe appended claims, which are incorporated into this section byreference.

Some embodiments of the present invention help reduce misalignmentscaused by heat and by mechanical pressures generated in attaching alaser diode assembly to other components, e.g. to a “cold plate” (aplate cooled via active cooling, e.g. by liquid or air or by athermo-electric cooler).

In some embodiments of the present invention, each laser diode, itsrespective collimating optics, and its turning mirror are assembled on aflat, heat-dissipating surface. Such surface will be called “opticalbench”. The optical bench has a high heat conductivity, and thus isroughly at a uniform temperature. Heat is absorbed below the benchsurfaces, so the temperature gradient is directed essentially downward.Consequently, each bench remains essentially flat and free of warpage,maintaining the angular orientation and vertical alignment between eachlaser diode and its respective collimating optics and turning mirror.

The inventor observed that the entire assembly of the laser diodes andthe optics should preferably be symmetric to reduce mechanical and otherdeformations in any given direction. Mechanical deformations may occurwhen the assembly is attached to some base (e.g. a cold plate) withfasteners which apply mechanical forces at selected points. Themechanical forces may deform the assembly, e.g. causing a bow betweenthe points of attachment. To limit the maximum bow, it is desirable forthe points of attachment to be about equidistant from each other. It isalso desirable to reduce the maximum distance between any point in theassembly and the closest point of attachment. This suggests a symmetricstructure, e.g. with rotational symmetry. In particular, the assemblyshould preferably be approximately circular or square in top view.

Given this structure, it is also desirable to lengthen the beam path soas to reduce the numerical aperture (NA) of the combined beam (the beamstack) entering the optical fiber. The reduced NA increases the combinedbeam's brightness and also facilitates fitting the combined beam intothe fiber's acceptance angle. In some embodiments, the beam path isincreased by extending the beam along at least three sides of a square(or a rectangle) running along the assembly periphery. For example, insome embodiments, the laser diodes are positioned in a row along a“first side” of the square. In a Cartesian coordinate system with an Xaxis positioned along this first side, the laser diodes emit beamspropagating along a YZ plane. Here X and Y are horizontal axes and Z isvertical. The Y axis provides the second side of the square path. Thebeams are collimated in their fast and slow axes as they travel alongthe YZ plane, i.e. along the second side. The collimating lenses areimmediately followed by turning mirrors which turn the respective beamsby about 90° to travel along the third side of the square. The beams areat different heights to form the beam stack. As soon as the beam stackis formed, i e immediately past the X coordinate of the last laser diode(or its submount), the beam stack hits another turning mirror. Thisturning mirror turns the beam stack by about 90° to travel along thesquare's fourth side. This turning mirror is immediately followed by afocusing optics that focuses the beam stack into the optical fiber'sinput. A highly compact structure is thus provided.

The invention is not limited to the features and advantages describedabove. Other features are described below. The invention is defined bythe appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a laser diode assembly according to someembodiments of the present invention.

FIG. 2 is a top view of the assembly of FIG. 1.

FIG. 3 is a perspective view of the assembly of FIG. 1 together withpackaging elements.

FIG. 4 is a perspective view of a laser diode assembly according to someembodiments of the present invention.

FIG. 5 is a side view of a laser diode assembly according to someembodiments of the present invention.

FIGS. 6, 7, 8 illustrate cross sections of laser beams in someembodiments of the present invention.

DESCRIPTION OF SOME EMBODIMENTS

The embodiments described in this section illustrate but do not limitthe invention. The invention is defined by the appended claims.

FIG. 1 is a perspective view of a laser diode assembly 110 according tosome embodiments of the present invention. FIG. 2 is a top view of theassembly. FIG. 3 is a perspective view of assembly 110 with packagingused in some embodiments. The assembly will be described with referenceto a Cartesian coordinate system XYZ where X and Y are horizontal axesand Z is vertical. However, the invention is not limited by anycoordinate system, and further the assembly 110 can be oriented andoperated in any position.

Assembly 110 includes three laser diodes 120.1, 120.2, 120.3 laterallyspaced from each other in the X direction. Any number of diodes can bepresent. In this embodiment, each diode 120.i (i=1,2,3) is asingle-emitter diode, formed in a discrete semiconductor structure, butthis is not necessary for the invention. Diodes 120 have horizontal pnjunctions. Each diode 120.i emits respective light beam 130.i (i=1,2,3)in the Y direction. The beams' slow axes are parallel to the X axis, andthe fast axes are parallel to the Z axis.

Each diode 120.i (i=1,2,3) is mounted on a respective submount 134.i inchip-on-submount (CoS) configuration. Each submount 134.i has highthermal conductivity, and can be dielectric or it can be conductive butelectrically insulated from diode 120.i. Suitable materials forsubmounts 134.i include ceramic materials common in semiconductorpackaging, for example Beryllia Ceramic or Aluminum Nitride used in CoSstructures available from Bookham, Lumics, INNOLUME and otherssemiconductor laser diode suppliers. These examples are not limiting.The submounts 134 (i.e. 134.1, 134.2, 134.3) provide first levelpackaging for the diode chips, and can be replaced with other types ofpackaging, whether known or to be invented. Each submount 134.i includeselectrical contacts (not shown) connected to the p and n type regions ofthe diode. These contacts connect the diode's p and n doped regions tothe respective two contact pads 138 provided on each submount 134.i(contact pads 138 are shown only for submount 134.1 for simplicity). Inoperation, a voltage is provided across the two pads 138 to cause lightemission by the respective diode.

Each submount 134.i is placed onto a respective optical bench 144.iwhich has high thermal conductivity. In the embodiment being described,the benches 144.i (i=1,2,3) are flat horizontal surfaces of a one-piececarrier 150 which can be made, for example, of copper or some othermetal or non-metal material having high thermal conductivity. Thesubmounts 134 are attached to benches 144 in a thermally conductivemanner, e.g. by thermally conductive adhesive such as a suitable epoxy,or by thermocompression, fasteners, and/or other means; to make benches144 effective in dissipating heat generated by the diodes. The submountsare located at a side 150.1 of carrier 150. The carrier is square in topview, with sides 150.1, 150.2, 150.3, 150.4. The opposite sides 150.1,150.3 are parallel to the XZ plane. The opposite sides 150.2, 150.4 areparallel to the YZ plane. In other embodiments, the carrier 150 isrectangular but not square. Non-rectangular carriers can also be used.For example, the carrier may have chamfered corners, or be circular, orof some other shape.

The benches 144.1, 144.2, 144.3 are positioned at different heights. Thebench 144.1 is stepped up by some distance h relative to bench 144.2,and the bench 144.2 is stepped up by distance h or some other distancerelative to bench 144.3.

A collimating lens 154.i (i=1,2,3) is attached to the respective opticalbench 144.i in front of the emitter of the respective diode 120.i tocollimate the diode's output beam 130.i along the fast axis. Anothercollimating lens 158.i is attached to bench 144.i farther down thebeam's path to collimate the beam along the slow axis. The beam'soptical axis is a straight or nearly straight line passing through therespective collimators 154.i, 158.i to the respective turning mirror162.i parallel to the Y axis. An insert A shows a collimated beam'scross section parallel to the XZ plane for beam 130.1 at the beam's exitfrom lens 158.1. The other beams can have the same shape.

Each turning mirror 162.i (i=1,2,3) is a vertical mirror attached to therespective bench 144.i near the carrier side 150.3 at an angle of about45° to each of the Y and X axes, to turn the respective beam 130.i byabout 90° (85° to 95° in some embodiments). The optical elements 154,158, 162 are attached to benches 144 with an adhesive (e.g. epoxy) orsome other means. Due to high conductivity of carrier 150, each bench'stemperature is highly uniform across the bench, and the bench remainshighly flat in thermal cycling. Therefore, the vertical alignmentbetween each diode 120.i and its respective optical elements 154.i,158.i, 162.i is highly stable.

After reflection from mirror 162.i, each beam 130.i travels parallel tothe X axis. Beam 130.1 passes above mirror 162.2 due the bench 144.1being higher (by distance h) than bench 144.2. Beams 130.1, 130.2 passabove mirror 162.3 for a similar reason. As beam 130.1 passes above eachmirror 162.2, 162.3, the beam 130.1 is joined by respective beams 130.2,130.3 to form a beam stack 130C, whose cross section parallel to the XYplane is shown in insert B. The individual beams 130.i overlie oneanother in the combined beam 130C, with their slow axes being horizontaland overlying one another. In some embodiments, the slow axes have thesame length and are aligned so that each upper axis is precisely aboveeach lower axis. In other embodiments, this precise alignment is absent,and further the slow axes may differ in length. In some embodiments, thecombined beam 130C has a square outline, but non-square outlines arealso possible. In some embodiments, the beams 130.i are placed as closeto each other as possible to reduce the numerical aperture of thecombined beam to obtain higher brightness.

The combined beam 130C is reflected by a vertical turning mirror 170 byabout 90° (85° to 95° in some embodiments). Mirror 170 is attached tocarrier 150 near the side 150.4 at an angle of about 45° to each of theYZ plane. After reflection from mirror 170, beam 130C travels along theY axis and enters focusing lens 174. Lens 174 converges the combinedbeam. After exiting the lens 174, the combined beam keeps travelingessentially along the Y axis into optical fiber 180. The focal distanceof focusing lens 174 is chosen to fit the beam 130C into a numericalaperture not exceeding the NA of fiber 180.

In FIG. 1, the optic elements 170, 174, 180 are attached to a separateoptical bench 144.4 of carrier 150. Bench 144.4 is below bench 144.3 toalign the beam 130C emerging from mirror 170 with the middle portion ofthe input surface of lens 174. Lens 174 has a circular cross sectionenclosing the square outline of beam 130C entering the lens. Fiber 180is mounted on bench 144.4 in a raised position so that the centers offiber 180 and lens 174 are at the same height. In other embodiments,bench 144.4 is level with bench 144.3 (i.e. the two benches are mergedinto a single flat surface). In such configuration, lens 174 can belowered into a groove in bench 144.4 to align the lens with beam 130C,and/or lens does not have to be circular, and/or the beams 130.i can becaused to rise upward on the way to lens 174 by tilting the mirrors 162and/or 170 by suitable angles. Other arrangements are also possible.

Optics 170, 174, 180 can be attached to carrier 150 by the same methodsas optics 154, 158, 162, or by some other techniques.

FIG. 2 (top view) illustrates dimensions obtained in some embodiments ofassembly 110. In these embodiments, each carrier 134.i is rectangular intop view, with the X and Y dimensions denoted as a and b respectively.The distance between the adjacent carriers 134.i is small, and assumedto be zero for the computation immediately below. The maximum length ofeach beam 130.i along the slow axis is reached at the entrance of lens158.i, and should not exceed a to ensure that the adjacent beams do notoverlap. (The beams could overlap, but they do not in the presentembodiment.) The maximum length at the entrance of each lens 158.i canbe smaller than a, and is set to aK₁ where K₁≦1 is a safety factorchosen to accommodate manufacturing and operational tolerances. In someembodiments, K₁ is at least ½, but can be any number. The beam's lengthfrom the emitter of diode 120.i to the entrance of lens 158.i istherefore about aK₁/[2NA_(S)], where NA_(S) is the beam's numericalaperture along the slow axis.

As seen from FIG. 2, the length of assembly 110 along the Y axis isabout

b+aK₁/[2NA_(S)]+aK₁  (1)

Along the X axis, the length of assembly 110 is about 3a plus thediameter of focusing lens 174. If there are N diodes, 3a should bereplaced by Na. The diameter of lens 174 should be at least the lengthof the diagonal of the square beam 130C as shown in insert C. The squarehas a side of aK₁, so the diameter is aK₁√{square root over (2)}. Thetotal length along the Y axis for an N diode assembly is therefore about

Na+aK₁√{square root over (2)}  (2)

The height of the structure is about the diameter of length 174, i.e.

aK₁√{square root over (2)}  (3)

The step h (FIG. 1) is chosen so that the individual beams 130.i do notoverlap in the combined beam 130C. The overlap could cause brightnessand power loss, but the overlap is acceptable in some embodiments. Ifthere is no overlap, the height of each beam 130.i in combined beam 130Cis given by the following equation:

height of bean 130.i=F _(f)·2NA _(f)  (4)

where F_(f) is the focal distance of each lens 154.i and NA_(f) is eachbeam's numerical aperture along the fast axis. The step h is chosen asequal or slightly above the height of beam 130.i, i.e.

h=K ₂ ·F _(f)·2NA _(f)  (5)

where K₂ is a safety factor, possibly a value from 1 to 3 inclusive.

To make the assembly square or near square, the X and Y dimensions (1)and (2) should be about equal. Setting (1) equal to (2) and solving forN, one can obtain a suitable range for the number of diodes based on thevalues a, b, NA_(S) and K₁. In some embodiments, the number N is in therange of 2 to 6 inclusive. This range is not limiting.

Further, multiple diodes can be manufactured in a single chip. Forexample, each diode 120.i can be replaced by a laser diode bar. In oneassembly 110, different diodes may generate different wavelengths, e.g.to generate colors by combining the wavelengths of different diodes.

During the assembly, each diode 120.i and its lenses 154.i, 158.i arealigned separately for each i using a far field camera. Optical fiber180 and focusing lens 174 are aligned together using a far field cameraand a light source in the far field. Then mirrors 162 are placed andaligned. Then mirror 170 is placed and aligned. Also, an additionalstructure (not shown) can be provided to carry a pair of commonterminals (not shown) one of which is electrically coupled to one ofcontacts 138 on each carrier 134.i to provide a positive voltage to thediodes. The other common terminal is electrically coupled to the otherone of contacts 138 on each carrier 134.i to provide a negative voltageto the diodes. This is an exemplary, not limiting arrangement, in whichthe diodes are interconnected in parallel. The diodes can alternativelybe connected in series, or not interconnected at all (e.g. to provideindependently controlled electric currents through different diodes ofdifferent wavelengths to generate multi-color images). The invention isnot limited to any electrical interconnections.

FIG. 3 illustrates suitable packaging for assembly 110. When theassembly 110 has been manufactured, carrier 150 is placed on the flat,middle portion of a base plate 310 made of a material having highthermal conductivity and low thermal deformation. Known copper alloyscan be used for this purpose. Carrier 150 is attached to base plate 310in a thermally conductive manner, e.g. by epoxy, thermocompression, orpossibly other means. In some embodiments, base 310 is square orcircular. Cylindrical housing 320 is fitted into a groove 330 made inthe top surface of base plate 310 around the position of the assembly110. Cylindrical housing 320 is rigidly fixed in the groove (withadhesive for example). Housing 320 includes an aperture (not shown) forfiber 180 and one or two apertures (not shown) for the common terminalscoupled to the contacts 138. One end of fiber 180 is threaded outwardthrough its respective aperture and is lengthened by attachment toanother fiber of a desired length. Electrical wires are threaded inthrough the respective apertures and attached to the respective commonterminals. The assembly is tested, and then a lid 340 is attached to thetop of housing 320 to provide a protective seal.

Base plate 310 has threaded holes 350 at its corners or at some otherplaces so that the adjacent holes 350 are about equidistant from eachother. Screws (not shown) are threaded through holes 350 to attach thebase plate to a cold plate 360 which can be actively cooled, for exampleby liquid, air, a thermo-electric cooler.

FIG. 4 shows another embodiment of diode assembly 110. This embodimentis similar to the embodiment of FIG. 1 but the optical benches 144.i arelevel with each other, i.e. are merged into a single horizontal surface144 at the top of carrier 150. The emitters of diodes 120 are all at thesame height, but optical prisms 410.i (i=1,2) with angled edges areplaced between respective fast axis collimators (FAC) 154.i and slowaxis collimators (SAC) 158.i to shift up the respective beam 130.i bythe desired height (e.g. height 2h for beam 130.1, height h for beam130.2). Therefore, the three beams 130.i reach the respective mirrors162.i at different heights, possibly the same heights as in FIG. 1.Mirrors 162 are mounted at respective different heights, possibly thesame respective heights as in FIG. 1, on appropriate submounts (notshown). Alternatively, the mirrors can be mounted directly on surface144 at the same height, but mirror 162.1 can be made taller than mirror162.2, and mirror 162.2 can be made taller than mirror 161.1. Beam 130.3can also be shifted up with a prism or other optics by a suitableamount. Other optic arrangements are also possible. In still otherembodiments with or without a single horizontal surface 144, the prisms410.i may be omitted and/or the beams may reach the mirrors 162 at thesame height but may be directed upward at respective different angles bymeans of the mirrors 162 (if the mirrors are not vertical for example)or by other optics so that the beams 130.i remain separate. In otherembodiments, the beams are merged together at least partially.

The remaining features can be as in any of the embodiments describedabove in connection with FIG. 1 (e.g. multiple-emitter diodes can beused, any number of diodes can be present, etc.).

In some variations of FIG. 1, two or more but less than all of benches144.i are merged together. Suitable optics control the height of eachbeam 130.i at the entrance of the respective mirror 162.i.

In FIG. 5, each bench 144.i (i=1,2, . . . ,N) is inclined at an angleα_(i) relative to the horizontal plane, where a₁>a₂> . . . >a_(N)≧0. Insome embodiments, a_(i)=a_(N)·(N−i+1). Lenses 154.i, 158.i and mirror162.i are attached to the optical bench 144.i in the same positionsrelative to the bench as in FIG. 1. Different mirrors 162.i are atdifferent heights due to the different inclination angles a_(i). Theangles and the positions and shapes of mirrors 162 are chosen to providea combined beam 130C as in insert B in FIG. 1 or 6. In FIG. 6, thecombined beam 130C is as in FIG. 1 but is rotated by some angle having avalue at least a_(N) and at most a₁. The angles a_(i) can be chosen sothat at the distance provided by equation (1) above and measured fromthe bottom of surfaces 144.i, the adjacent beams are vertically shiftedby the h value of equation (5) relative to each other. The value a₁ isthen about

a ₁ =h/L

where L is given by (1).

The slow axes of beams 130.i may be non-horizontal as in FIGS. 6, 7,and/or may not be parallel to each other as in FIG. 7, and/or may beshifted relative to each other along their slow axes, e.g. may overlaponly partially when projected onto a horizontal plane (FIG. 8).

Some embodiments provide an apparatus disposed in a region having aplurality of vertical sides comprising at least a first side, a secondside, a third side, and a fourth side. For example, in FIG. 1, theregion containing the assembly 110 may be defined as enclosed by thefirst, second, third, and fourth sides which include the respectivesides 150.1, 150.2, 150.3, 150.4. Alternatively, the region may bedefined as having more than four sides, e.g. the assembly 110 may beenclosed into a pentagonal region. In any case, each of the second andfourth sides is between the first side and the third side, and each ofthe first and third sides is between the second side and the fourthside. The apparatus, and hence the region, contains a plurality of laserdiodes arranged to emit laser beams into the region in a direction ordirections away from the first side (e.g. away from side 150.1 in FIG.1, 4 or 5), wherein the laser diodes' emitters are at differentdistances from at least one of the second and fourth sides (e.g. fromside 150.2 and/or 150.4 in FIG. 1). Each laser beam may be a continuousbeam (as in insert A of FIG. 1), or may be a combined discontinuous beamof multiple laser diodes, e.g. of two or more diodes of a laser diodebar. Each beam includes a continuous or discontinuous slow axis. Theapparatus further comprises optics for directing the laser beams to anoutput window. The output window may or may not be an input of anoptical fiber. The optics comprises collimator optics (e.g. 154.1,154.2, 154.3, 158.1, 158.2, 158.3) for collimating the laser beams.Also, a first beam-redirector is provided (e.g. 162.1, 162.2, 162.3) fordirecting the collimated beams to travel adjacent to the third side withthe beams' slow axes overlying one another in a vertical cross sectiontransverse to the beams (e.g. as in insert B in FIG. 1). A secondbeam-redirector (e.g. 170) directs the beams received from the firstbeam-redirector to travel adjacent to the fourth side. Focusing optics(e.g. 174) converges the beams traveling from the second redirector tothe output window.

In some embodiments, the first side is at an angle of 71° to 109° to thesecond side, the second side is at an angle of 71° to 109° to the thirdside, the third side is at an angle of 71° to 109° to the fourth side,and the fourth side is at an angle of 71° to 109° to the first side.

In some embodiments, the region is rectangular in top view, with a ratioof lengths of any two adjacent sides being at least 0.7 and at most1.45.

In some embodiments, the laser diodes and the optics are arranged tokeep the beams separate from each other (i.e. the beams do not merge) atleast between the laser diodes and the first beam-redirector.

In some embodiments, in a first cross section parallel to the first sideand located at an entrance to the first beam-redirector (e.g. in avertical cross section right before the mirrors 162), the beams' slowaxes do not overlie one another. Alternatively, at least some of thebeams' slow axes may overlie one another but do not overlap as much asat the exit from the first beam-redirector. The first beam-redirectorthus increases the beam overlap. For example, in FIG. 1, the beampositions at the exit of mirrors 162 (the exit of mirror 162.3) isillustrated in insert B. The overlap between any two slow axes can bemeasured in an orthogonal projection of one of the slow axes onto theother. Mirrors 162 increase the overlaps.

Some embodiments comprise a plurality of laser diode structures, eachlaser diode structure comprising a discrete semiconductor structurecomprising one or more of said laser diodes. For example, a discretesemiconductor structure can be a laser diode bar. Further, a pluralityof generally flat, heat-dissipating surface regions is provided (e.g.optical benches 144.i) for dissipating heat generated by the laserdiodes, each laser diode structure being rigidly attached to acorresponding one of the flat, heat dissipating surface regions. Eachlaser diode structure is associated with a portion of the collimatingoptics and the first beam-redirector for collimating and directing thebeam or beams emitted by the laser diode structure, the portion beingrigidly attached to the corresponding flat, heat-dissipating surfaceregion, wherein the portions being spaced from each other.

The invention is not limited to the features and advantages describedabove except as defined by the appended claims. Other embodiments andvariations are within the scope of the invention, as defined by theappended claims.

1. An apparatus comprising: (1) a thermally dissipative body comprisinga top surface comprising a plurality of heat-dissipating surfaceregions; (2) a plurality of laser diode structures, each laser diodestructure comprising a discrete semiconductor structure comprising oneor more laser diodes, the laser diode structures being separate fromeach other; wherein each said laser diode structure overlies, and isrigidly attached to, a respective one of the heat-dissipating surfaceregions, and each laser diode structure's attachment to the top surfaceis confined to the respective heat-dissipating surface region and isseparate from the attachment of every other one of the laser diodestructures to the top surface; wherein each said laser diode structure'sone or more laser diodes are positioned to emit one or more laser beamsabove the top surface; (3) fast-axis collimator optics for collimatingthe laser beams emitted by the laser diode structures; (4) slow-axiscollimator optics comprising, for each said laser diode structure, oneor more slow-axis collimators for collimating the one or more laserbeams emitted by the laser diode structure, wherein the one or moreslow-axis collimators of each laser diode structure are separate fromthe one or more slow-axis collimators of every other laser diodestructure; wherein for each laser diode structure, the corresponding oneor more slow-axis collimators overlie, and are rigidly attached to, thelaser diode structure's heat-dissipating surface region, and the one ormore slow-axis collimators' attachment to the top surface is confined tothe respective heat-dissipating surface region and is separate from theattachment of every other slow-axis collimator to the top surface; (5) afirst beam-redirector comprising, for each said laser diode structure, afirst beam-redirector portion for redirecting one or more collimatedlaser beams which are emitted by the laser diode structure andcollimated by the fast-axis collimator optics and the laser diodestructure's one or more slow-axis collimators, wherein the firstbeam-redirector portions are separate from each other; wherein the firstbeam-redirector reduces a lateral spread of slow axes of the collimatedlaser beams in a vertical cross section perpendicular to an optical axisof at least one collimated laser beam, wherein in at least one verticalcross section perpendicular to the optical axis of at least one thecollimated laser beam redirected by the first beam-redirector, the slowaxes of the collimated laser beams redirected by the firstbeam-redirector spread laterally and overlie one another; wherein foreach laser diode structure, the corresponding first beam-redirectorportion overlies, and is rigidly attached to, the laser diodestructure's heat-dissipating surface region, and the firstbeam-redirector portion's attachment to the top surface is confined tothe respective heat-dissipating surface region and is separate from theattachment of every other first beam-redirector portion to the topsurface; wherein all said attachments to the top surface are thermallydissipative for the heat-dissipative body to dissipate heat generated bythe laser diodes, the fast-axis and slow-axis collimator optics, and thefirst-beam redirector.
 2. The apparatus of claim 1 wherein theheat-dissipative body is for conducting heat downward from the topsurface to an active cooler.
 3. The apparatus of claim 2 in combinationwith the active cooler attached to the body below the body.
 4. Theapparatus of claim 1 wherein at least one said attachment uses asubmount and/or adhesive.
 5. The apparatus of claim 1 wherein thefast-axis collimator optics comprises, for each said laser diodestructure, one or more fast-axis collimators for collimating the laserbeams emitted by the laser diode structure, wherein the one or morefast-axis collimators of each laser diode structure are separate fromthe one or more fast-axis collimators of every other laser diodestructure; wherein for each said laser diode structure, thecorresponding one or more fast-axis collimators overlie, and are rigidlyattached to, the laser diode structure's heat-dissipating surfaceregion, and the one or more fast-axis collimators' attachment to the topsurface is thermally dissipative and is confined to the respectiveheat-dissipating surface region and is separate from the attachment ofevery other fast-axis collimator to the top surface.
 6. The apparatus ofclaim 1 wherein the laser diodes, the fast-axis and slow-axis collimatoroptics, and the first beam-redirector are arranged to keep the laserbeams separate from each other at least between the laser diodes and thefirst beam-redirector.
 7. The apparatus of claim 1 wherein the laserdiodes, the fast-axis and slow-axis collimator optics, and the firstbeam-redirector are arranged to keep the laser beams separate from eachother at least between the laser diodes and an output of the firstbeam-redirector.
 8. The apparatus of claim 1 wherein the first beamredirector is arranged to turn each collimated beam by an angle of 71°to 109° when viewed from the top.
 9. A method for manufacturing theapparatus of claim 1, the method comprising assembling together thebody, the laser diode structures, the fast-axis and slow-axis collimatoroptics, and the first beam redirector.
 10. A method for operating anapparatus which comprises: (1) a thermally dissipative body comprising atop surface comprising a plurality of heat-dissipating surface regions;(2) a plurality of laser diode structures, each laser diode structurecomprising a discrete semiconductor structure comprising one or morelaser diodes, the laser diode structures being separate from each other;wherein each said laser diode structure overlies, and is rigidlyattached to, a respective one of the heat-dissipating surface regions,and each laser diode structure's attachment to the top surface isconfined to the respective heat-dissipating surface region and isseparate from the attachment of every other one of the laser diodestructures to the top surface; wherein each said laser diode structure'sone or more laser diodes are positioned to emit one or more laser beamsabove the top surface; (3) fast-axis collimator optics for collimatingthe laser beams emitted by the laser diode structures; (4) slow-axiscollimator optics comprising, for each said laser diode structure, oneor more slow-axis collimators for collimating the one or more laserbeams emitted by the laser diode structure, wherein the one or moreslow-axis collimators of each laser diode structure are separate fromthe one or more slow-axis collimators of every other laser diodestructure; wherein for each laser diode structure, the corresponding oneor more slow-axis collimators overlie, and are rigidly attached to, thelaser diode structure's heat-dissipating surface region, and the one ormore slow-axis collimators' attachment to the top surface is confined tothe respective heat-dissipating surface region and is separate from theattachment of every other slow-axis collimator to the top surface; (5) afirst beam-redirector comprising, for each said laser diode structure, afirst beam-redirector portion for redirecting one or more collimatedlaser beams which are emitted by the laser diode structure andcollimated by the fast-axis collimator optics and the laser diodestructure's one or more slow-axis collimators, wherein the firstbeam-redirector portions are separate from each other; wherein the firstbeam-redirector reduces a lateral spread of slow axes of the collimatedlaser beams in a vertical cross section perpendicular to an optical axisof at least one collimated laser beam, wherein in at least one verticalcross section perpendicular to the optical axis of at least one thecollimated laser beam redirected by the first beam-redirector, the slowaxes of the collimated laser beams redirected by the firstbeam-redirector spread laterally and overlie one another; wherein foreach laser diode structure, the corresponding first beam-redirectorportion overlies, and is rigidly attached to, the laser diodestructure's heat-dissipating surface region, and the firstbeam-redirector portion's attachment to the top surface is confined tothe respective heat-dissipating surface region and is separate from theattachment of every other first beam-redirector portion to the topsurface; wherein all said attachments to the top surface are thermallydissipative for the heat-dissipative body to dissipate heat generated bythe laser diodes, the fast-axis and slow-axis collimator optics, and thefirst-beam redirector; the method comprising: emitting the laser beamsby the laser diodes; and actively cooling the body's region locatedbelow the top surface to cause downward heat conduction from the topsurface to the body's region.
 11. An apparatus comprising: a pluralityof laser diode structures, each laser diode structure comprising adiscrete semiconductor structure comprising one or more laser diodes; aplurality of heat-dissipating surface regions for dissipating heatgenerated by the laser diodes, each laser diode structure being rigidlyattached to a corresponding one of the heat-dissipating surface regions,wherein in each pair of the heat-dissipating surface regions, one of theheat-dissipating surface regions of the pair is either higher or lowerthan the other one of the heat-dissipating surface regions of the pair;for each said laser diode structure, one or more collimators forcollimating one or more laser beams emitted by the one or more diodes ofthe laser diode structure; a first beam-redirector comprising, for eachsaid laser diode structure, a first beam-redirector portion forredirecting the one or more collimated laser beams, the firstbeam-redirector being for positioning the beams with their slow axesoverlying each other; wherein for each laser diode structure, its firstbeam-redirector portion overlies, and is rigidly attached to, thecorresponding heat-dissipating surface region but does not overlie anyother one of the heat-dissipating surface regions.
 12. The apparatus ofclaim 11 wherein for each laser diode structure, each of thecorresponding one or more collimators is rigidly attached to thecorresponding heat-dissipating surface region but does not overlie anyother one of the heat-dissipating surface regions.
 13. The apparatus ofclaim 11 wherein the heat-dissipating surface regions are arranged tothermally communicate with an active cooler arranged for conducting heatdownward from the heat-dissipating surface regions.
 14. The apparatus ofclaim 13 in combination with the active cooler positioned below theheat-dissipating surface regions.
 15. The apparatus of claim 11 whereinthe one or more collimators comprise, for each said laser diodestructure, one or more slow-axis collimators for collimating the laserbeams emitted by the laser diode structure, wherein the one or moreslow-axis collimators of each laser diode structure are separate fromthe one or more slow-axis collimators of every other laser diodestructure; wherein for each said laser diode structure, thecorresponding one or more slow-axis collimators overlie, and are rigidlyattached to, the laser diode structure's heat-dissipating surfaceregion.
 16. The apparatus of claim 11 wherein the laser diodes, thecollimators, and the first beam-redirector are arranged to keep thelaser beams separate from each other at least between the laser diodesand the first beam-redirector.
 17. The apparatus of claim 11 wherein thelaser diodes, the collimators, and the first beam-redirector arearranged to keep the laser beams separate from each other at leastbetween the laser diodes and an output of the first beam-redirector. 18.The apparatus of claim 11 wherein the first beam redirector is arrangedto turn each collimated beam by an angle of 71° to 109° when viewed fromthe top.
 19. A method for manufacturing the apparatus of claim 11, themethod comprising assembling together the heat-dissipating surfaceregions, the laser diode structures, the collimators, and the first beamredirector.
 20. A method for operating an apparatus which comprises: aplurality of laser diode structures, each laser diode structurecomprising a discrete semiconductor structure comprising one or morelaser diodes; a plurality of heat-dissipating surface regions fordissipating heat generated by the laser diodes, each laser diodestructure being rigidly attached to a corresponding one of theheat-dissipating surface regions, wherein in each pair ofheat-dissipating surface regions, one of the heat-dissipating surfaceregions of the pair is either higher or lower than the other one of theheat-dissipating surface regions of the pair; for each said laser diodestructure, one or more collimators for collimating one or more laserbeams emitted by the one or more diodes of the laser diode structure; afirst beam-redirector comprising, for each said laser diode structure, afirst beam-redirector portion for redirecting the one or more collimatedlaser beams, the first beam-redirector being for positioning the beamswith their slow axes overlying each other; wherein for each laser diodestructure, its first beam-redirector portion overlies, and is rigidlyattached to, the corresponding heat-dissipating surface region but doesnot overlie any other one of the heat-dissipating surface regions; themethod comprising: emitting the laser beams by the laser diodes; andactively cooling a first region located below the heat-dissipatingsurface regions to cause downward heat conduction from theheat-dissipating surface regions.
 21. An apparatus disposed in a regionhaving a plurality of vertical sides comprising at least a first side, asecond side, a third side, and a fourth side, wherein each of the secondand fourth sides is between the first side and the third side, and eachof the first and third sides is between the second side and the fourthside, the apparatus comprising: (1) a plurality of laser diodes arrangedto emit laser beams into the region in a direction or directions awayfrom the first side, wherein the laser diodes' emitters are at differentdistances from at least one of the second and fourth sides; and (2)optics for directing the laser beams to an output window, the opticscomprising: (2a) collimator optics for collimating the laser beams; (2b)a first beam-redirector for directing the collimated beams to traveladjacent to the third side with the beams' slow axes overlying oneanother in a vertical cross section transverse to the beams; (2c) asecond beam-redirector for directing the beams received from the firstbeam-redirector to travel adjacent to the fourth side; and (2d) focusingoptics for converging the beams traveling from the second redirector tothe output window.
 22. The apparatus of claim 21 wherein the first sideis at an angle of 71° to 109° to the second side, the second side is atan angle of 71° to 109° to the third side, the third side is at an angleof 71° to 109° to the fourth side, and the fourth side is at an angle of71° to 109° to the first side.
 23. The apparatus of claim 21 wherein theregion is rectangular in top view, with a ratio of lengths of any twoadjacent sides being at least 0.7 and at most 1.45.
 24. The apparatus ofclaim 21 wherein the laser diodes and the optics are arranged to keepthe beams separate from each other at least between the laser diodes andthe first beam-redirector.
 25. The apparatus of claim 21 wherein in afirst cross section parallel to the first side and located at anentrance to the first beam-redirector, the beams' slow axes do notoverlie one another or, if any slow axes overlie one another, an overlapbetween such slow axes is smaller than at an exit from the firstbeam-redirector in a second cross section orthogonal to the third side.26. The apparatus of claim 21 comprising: a plurality of laser diodestructures, each laser diode structure comprising a discretesemiconductor structure comprising one or more of said laser diodes; aplurality of generally flat, heat-dissipating surface regions fordissipating heat generated by the laser diodes, each laser diodestructure being rigidly attached to a corresponding one of the flat,heat dissipating surface regions; wherein each laser diode structure isassociated with a portion of the collimating optics and the firstbeam-redirector for collimating and directing the beam or beams emittedby the laser diode structure, the portion being rigidly attached to thecorresponding flat, heat-dissipating surface region, wherein theportions being spaced from each other.
 27. The apparatus of claim 21wherein the output window is an input of an optical fiber.
 28. Theapparatus of claim 21 wherein the first beam-redirector is for directingthe collimated beams to travel adjacent to the third side with thebeams' slow axes overlying one another and not lying on a singlestraight line.
 29. The apparatus of claim 21 wherein the firstbeam-redirector is for directing the collimated beams to travel adjacentto the third side with the beams' slow axes overlying one another andparallel to each other in the vertical cross section transverse to thebeams.
 30. The apparatus of claim 21 wherein the collimator optics andthe first beam redirector are for directing the beams not to overlapwhen travelling adjacent to the third side.
 31. A method formanufacturing the apparatus of claim 21, the method comprising mounting,in said region, the laser diodes and the optics for directing the laserbeams.
 32. An apparatus comprising: (1) a plurality of laser diodesarranged to emit laser beams whose optical axes do not overlie eachother; (2) optics for directing the laser beams to an output window, theoptics comprising: (2a) collimator optics for providing a plurality ofcollimated beams, each collimated beam being produced by collimating acorresponding beam emitted by the laser diodes; (2b) a firstbeam-redirector for turning each collimated beam in a directionpositioned in top view at an angle of 71° to 109° to the optical axis ofthe corresponding beam emitted by the laser diodes, and for positioningthe beams' slow axes to overlie one another in a vertical cross sectiontransverse to the beams; (2c) a second beam-redirector for turning thebeams received from the first beam-redirector, wherein in top view thebeams entering the second beam-redirector form an angle or angles of 71°to 109° to the beams emerging from the second beam-redirector; and (2d)focusing optics for converging the beams traveling from the secondredirector to the output window.
 33. The apparatus of claim 32 whereinin top view, for each said beam, the beam's path to the firstredirector, the beam's path from the first redirector to the secondredirector, and the beam's path between the second redirector and theoutput window are arranged on third sides of a rectangle, and in thelargest of said rectangles, a ratio of lengths of any two adjacent sidesis at least 0.7 and at most 1.45.
 34. The apparatus of claim 32 whereinthe laser diodes and the optics are arranged to keep the beams separatefrom each other at least between the laser diodes and the firstbeam-redirector.
 35. The apparatus of claim 32 wherein in a firstvertical cross section transverse to the beams and located at anentrance to the first beam-redirector, the beams' slow axes do notoverlie one another or, if any slow axes overlie one another, an overlapbetween such slow axes is smaller than in a second cross sectionorthogonal to the beams exiting the first beam-redirector.
 36. Theapparatus of claim 32 comprising: a plurality of laser diode structures,each laser diode structure comprising a discrete semiconductor structurecomprising one or more of said laser diodes; a plurality of generallyflat, heat-dissipating surface regions for dissipating heat generated bythe laser diodes, each laser diode structure being rigidly attached to acorresponding one of the flat, heat dissipating surface regions; whereineach laser diode structure is associated with a portion of thecollimating optics and the first beam-redirector for collimating anddirecting the beam or beams emitted by the laser diode structure, theportion being rigidly attached to the corresponding flat,heat-dissipating surface region, wherein the portions being spaced fromeach other.
 37. The apparatus of claim 32 wherein the output window isan input of an optical fiber.
 38. The apparatus of claim 32 wherein thefirst beam-redirector and the second beam redirector are for turningeach collimated beam in a direction positioned in top view at a combinedangle of 71°+71°=142° to 109°+109°=218° relative to the optical axis ofthe corresponding beam emitted by the diodes.
 39. The apparatus of claim32 wherein the collimator optics and the first beam redirector are fordirecting the beams not to overlap at least until entering the secondbeam-redirector.
 40. A method for manufacturing the apparatus of claim32, the method comprising: arranging the laser diodes to emit laserbeams whose optical axes do not overlie each other; and arranging theoptics for directing the laser beams to provide the collimated beams, toturn each collimated beam by the first beam-redirector, to turn thebeams received from the first beam-redirector by the secondbeam-redirector, and to converge the beams travelling from the secondredirector by the focusing optics.